Organisms control antibody production at multiple steps during an immune response and this response must be carefully adjusted to the invading pathogen. If the response is excessive, autoimmune defects can damage host tissues, whereas if it is inadequate, the pathogen may persist and threaten survival. Soluble factors have been identified that stimulate the humoral immune response, but our knowledge of negative regulators of this process has been quite limited (Ravetch et al., 2000, Science 290:84). Indeed, few soluble cytokines have been identified whose loss of function leads to enhanced antibody production.
During the humoral immune response, a complex set of signaling events orchestrate antibody production. The process begins with antigen presentation to mature peripheral B cells, which proliferate and migrate to germinal centers. Cells possessing B cell receptors with the highest affinity for antigen are favored to survive while their low-affinity counterparts more readily undergo apoptosis. The activated B cells which survive this selection differentiate into memory B cells or antibody-secreting plasma cells. Many B cells also secrete antibody outside of the germinal center selection process in the extrafollicular response (MacLennan et al., 2003, Immunol Rev 194:8). Extrafollicular responses are thought to be important following exposure to T-independent antigens (Fagarasan et al., 2000, Science 290:89; Martin et al., 2001. Immunity 14:617). Once the antigen has been removed, B cells return to a resting state. Turning off B cell activation is necessary both for homeostatic resetting of antibody secretion and also for preventing pathologic autoimmune conditions. Little is known about the soluble factors which control the deactivation process.
The fibroblast growth factor (FGF) family of extracellular regulators has been shown to control the physiology and development of virtually all higher vertebrate tissues. Twenty-three FGF ligands have been identified in mammals, and these ligands interact with cell surface receptors encoded by five different genes (Wiedemann et al., 2000, Genomics 69:275; Ornitz et al., 2001, Genome Biol 2). Alternative splicing in the ligand-binding domain generates variable forms of the FGF receptors, thereby increasing diversity.
FGF2, or basic FGF, was the first identified FGF family member (Abraham et al., 1986, Embo J 5:2523) and is one of the most extensively studied. Expressed in most embryonic and adult tissues, it exists in high and low molecular weight isoforms due to initiation of translation at alternative start sites. It binds to all five receptors with preference for the “c” alternate splice form of receptors 1-3 (Ornitz et al, 1996, J Biol Chem 271:15292). FGF2 has been shown to stimulate widely varying effects, including proliferation, differentiation, apoptosis, and migration. Consequently, the FGF2 signal is interpreted differently depending on cellular context.
U.S. Pat. No. 4,994,559 discloses human basic fibroblast growth factor.
U.S. Pat. No. 5,229,501 discloses expression and use of human fibroblast growth factor receptor.
U.S. Pat. No. 5,288,855 discloses an extracellular form of human fibroblast growth factor receptor.
U.S. Pat. No. 5,707,632 discloses receptors for fibroblast growth factors.
U.S. Pat. No. 5,891,655 discloses methods for identifying molecules that regulate FGF activity and oligosacharide modulators of FGF receptor activation.
U.S. Pat. No. 6,071,885 discloses treatment of FGF-mediated conditions by administration of cardiac glycoside and aglycone derivatives thereof.
U.S. Pat. No. 6,350,593 discloses receptors for fibroblast growth factors and methods for evaluating compositions for antagonism to fibroblast growth factors and fibroblast growth factors receptors.
U.S. Pat. No. 6,255,454 discloses expression and use of a human fibroblast growth receptor and a soluble version of the receptor.
U.S. Pat. No. 6,900,053 discloses antisense modulation of fibroblast growth factor receptor 2 expression.
Multiple human therapeutics are designed to enhance the immune response, but their use in humans are complicated by severe side effects. For example, exogenous IL-2 is administered to patients with advanced melanoma in order to stimulate the antitumor immune response. But this biologic, acting as a systemic cytokine which directly activates T cells, is beset by harsh side effects, such as dangerous hypotension. What is needed are new methods for enhancing immune function and, in particular, humoral immunity.